1. Field of the Invention
The present invention relates to a color image processing apparatus, a method therefor, and a printer driver.
2. Related Background Art
For a color printing apparatus in general, a colorimetric color reproduction is used for reproducing the color of an inputted color image. The colorimetric color reproduction represents a case where the chromaticity of the colors of an original image and its reproduced image is equal, and the interrelated luminance thereof is also equal. In this case, the spectral reflection factors of these images are different. Thus, the reproduction will be conditionally isochromatic. This color reproduction method is one of the effective methods under a certain observational condition because it will suffice if only the colorimetric values X, Y, and Z (three stimulus values of an object color) obtainable by a spectro-colorimeter or the like are the same in an original image and its reproduced image.
For example, if an original image is a RGB luminance data which should be reproduced by ink materials or toners of Cy (cyanogen) Mg (magenta), Ye (yellow), and Bk (black), the conversion of the Cy, Mg, Ye, and Bk density data from the RGB luminance, namely, the color reproduction process, is dependent on the output characteristics of a printer (output method and the characteristics of toner or ink). In other words, if the characteristics of toner or ink are different, the color reproduction process will be different accordingly. Therefore, a Gamma correction and/or color masking process will be performed.
FIG. 2 is a block diagram showing the fundamental circuit of a color reproduction processing circuit of a color printer. A density conversion circuit 50 performs the logarithmic conversion of the RGB luminance of an inputted image and outputs the density data of Cy, Mg, and Ye. An under color removal circuit 52 forms the Bk data from the Cy, Mg, and Ye density data from the density conversion circuit 50 and removes the under color. A masking circuit 54 performs the masking process for the Cy, Mg, and Ye density data in order to remove the mutual influence of the unwanted absorption characteristics of the ink materials or toners. A .gamma. conversion circuit 56 performs the .gamma. conversion of the Cy, Mg, and Ye density data output from the masking circuit 54 and the Bk data from the under color removal circuit 52, and adjusts the contrast and brightness.
In this respect, the processing parameters for the circuits 50 to 54 are set per printer, and are fixed values.
When a color image is output to a monitor and a printer, the output image on the monitor and the one on the printer appear in different color due to the difference in characteristics if the same image data are supplied to the color monitor and the printer. As a method for adjusting the color appearance of a printed image, there are known a Gamma correction method wherein an image data to be supplied to a printer is Gamma corrected in advance, and an input masking method wherein the image data are adjusted by a matrical operation.
As shown in FIG. 3, according to a Gamma correction method, the RGB luminance data are Gamma corrected by a Gamma correction circuit 58. Then, a color reproduction process is given by a color reproduction processing circuit 60 to the output from the Gamma correction circuit 58. The color reproduction processing circuit 60 is structured as shown in FIG. 2. FIG. 4 illustrates the input and output characteristics of the Gamma correction circuit 58 and its operational expression.
As shown in FIG. 5, according to an input masking method, the RGB luminance data are processed by an input masking of the masking circuit 62. Then, a color reproduction process is given to the output from the input masking circuit 62. The color reproduction processing circuit 64 is structured as shown in FIG. 2 in the same manner as the color reproduction processing circuit 60. The operational expression for the input masking circuit 62 is shown in FIG. 6. In FIG. 6, reference marks Rin, Gin, and Bin designate input; Rout, Gout, and Bout, output and a11, a12, a13, a21, a22, a23, a31, a32, and a33 conversion coefficient, respectively.
Gamma correction and/or input masking process such as these have hitherto been executed on the side of an apparatus which outputs image data (a computer, for example). A printer driver, which is a printer control software for a computer, serves to execute the Gamma correction and/or input masking correction, for example. A problem is encountered here that this processing load is heavy for the printer driver.
Particularly, not only various monitor apparatuses which are connectable are on the market, but also various color printers are on the market at present. As a result, the printer driver is inevitably required to bear a heavier load, leading to a slow down of its processing speed. Also, when a color image is displayed on a display monitor or printed out onto a recording sheet, the output image on the monitor and the printed image appear in different color due to the coloring characteristics genuine to the apparatuses if the same image data are output to the color monitor display and a printer as they are.
Therefore, as a method to adjust the color appearance of a printed image, there have been known a .gamma. correction method to give a .gamma. correction in advance to the image data which are output to a printer, and an input masking method to adjust them by a matrical operation.
Nevertheless, according to the above-mentioned conventional example, a user must select and set a .gamma. value or an input masking coefficient in order to perform a color correction for the printer output in accordance with the characteristics of the monitor display apparatus when the menu setting is executed for a printer driver. As a result, the user must check and reset the .gamma. value or input masking coefficient which corresponds to the characteristics of the monitor display whenever the connectable monitor display apparatuses are replaced. Thus, the problem of an inefficient operativity is encountered.
Particularly, when various connectable monitor display apparatuses are currently available on the market, a user must bear a heavy burden in terms of the adjustment that he should make for the output characteristics in consideration of the characteristics of the display apparatus obtained from the market.